The invention relates to an electrode for contacting electrically conductive surfaces, in particular for contacting one or a plurality of photovoltaic (PV) elements being part of a photovoltaic cell or solar cell. The invention further relates to photovoltaic cells produced with this electrode.
The generation of electrical energy using photovoltaic technology has reached a high standard. However, the production of PV cells and PV modules is still rather complicated and expensive. Also the efficiency of energy generation using PV modules with a maximum efficiency of about 17 percent is rather low. From an economic point of view the generation of electric power using photovoltaic technology is only acceptable under current conditions if it is supported and/or subsidized by some means, e.g. by the so called 100 000-roofs program in Germany or similar programs in California, USA. Thus, in the field of photovoltaic technology there still remains a critical requirement to lower the production costs and enhance the efficiency of the energy generation using PV elements and PV modules.
Commonly used PV cells comprise a semiconductor element with a junction of the type (n+n (or p) p+) on the basis of mono- or multicrystalline silicon, amorphous silicon and other thin-film semiconductors with an embedded p-n junction. One surface of the element is usually covered with a metal layer, such as aluminum or stainless steel, while the other surface is provided with an anti-reflective coating. Both surfaces are in contact with electrodes, which collect and carry off the generated electrical energy. This structure is embedded between transparent protective layers, such as glass.
The electrodes are all produced using screen-printing technology. However, electrodes produced this way have a high series resistance. Apart from this, expensive devices and equipment are required for the production and cost reduction is limited when this technology is employed.
From the patent U.S. Pat. No. 5,759,291 A (Inchinose et. al.) a semiconductor element (wafer) with parallel metallic contact or current collecting wires (electrodes) which are fixed to the surface of the element by means of a conductive adhesive, in which conductive particles are dispersed is known. These electrode wires are arranged in parallel between connecting conductors which are running along the edges of the element. For this type of electrode the ohmic contact resistance between the semiconductor surface and the wires is relatively high, which results in a high energy loss and a low efficiency especially under concentrated solar radiation. Also, the production of such PV cells is rather complicated.
From the patent U.S. Pat. No. 5,084,107 A (Deguchi et. al.) a similar solar cell and array of solar cells are known, wherein metallic electrode wires are adhered to the surface of the photovoltaic element by means of an adhesive material. In the adhesive, conductive particles are dispersed. Also with this electrode structure, the production costs and the contact resistance between the wires and the surface of the element are fairly high.
From the patent U.S. Pat. No. 5,158,618 A (Rubin et al.) an electrode structure is known, wherein the contact wires are embedded in a transparent polymer block in such a way, that they partly protrude from the polymer block. Said electrodes contact the element from one or from two sides and are sandwiched between transparent protective layers, such as glass. As the wires of the electrode are, for example, configured as coils, there are only point contacts between the wires and the surface of the PV element. Thus, also in this case the series resistance of a PV cell is relatively high. Also the production costs are relatively high, since the automated production of such types of solar cells and PV modules is not possible.